1. Field of the Invention
The present invention relates to a personal computer cooling device for cooling an electronic element such as a processing unit of a personal computer by means of a heat pipe for transmitting the heat as the latent heat of a working fluid, and a process for manufacturing a container for the heat pipe.
2. Related Art
In recent years, a variety of personal computers have been desired to have their sizes and weights reduced. These reductions have seriously limited such a space in the personal computer as to be occupied by the cooling device. On the other hand, the output of the processing unit is augmented year by year as the number of functions is increased and as the processing speed is improved. In the prior art, heat pipes having an excellent heat transmission capacity have been noted as the cooling device. Of these, a plate heat pipe having a flattened container is widely adopted because it satisfies the conditions for the contact with the processing unit and the saving of space.
One example of the personal computer cooling device of the prior art is shown in FIGS. 33 and 34. In FIG. 33, a personal computer body 1 is a relatively thin, rectangular box made of a plastic panel or a metal panel and given a size of about A5 to A4 according to the JIS (i.e., Japanese Industrial Standard). The personal computer body 1 is equipped on its upper face with a keyboard section 2 and a display section 3. These keyboard section 2 and the display section 3 are individually hinged, as indicated at 2a and 3a, to the personal computer body 1. In other words, the keyboard section 2 and the display section 3 can be turned up from and down to the personal computer body 1. Moreover, these keyboard and display sections 2 and 3 are individually equipped with electromagnetic insulating plates 4 having equal sizes. These electromagnetic insulating plates 4 are made of an aluminum sheet.
In the front half (as located at the side of the keyboard section 2 in FIG. 33) of the space in the personal computer body 1, there are mounted a detachable hard disk drive 5, a floppy disk drive, a battery, an add-in memory (although all of them are not shown) and so on. In the bottom of the other half space of the personal computer body 1, on the other hand, there is arranged a heat pipe 6. Over this heat pipe 6, there is laid through a heat transmission promoting compound a central processing unit (as will be shortly referred to as the "CPU") 7, which in turn are overlaid by a plurality of printed circuits 8.
The aforementioned heat pipe 6 is a plate heat pipe having a flattened hollow container which is equipped on its portion with a plurality of rectangular fins 9 for retaining the heat radiating area. Moreover, the container of this heat pipe 6 is formed in its wall face with a plurality of (not-shown) grooves which extend in the longitudinal direction to act as wicks.
In the cooling device thus constructed, the working fluid in the heat pipe 6 is evaporated by the heat which is generated from the CPU 7 as the personal computer is used, and the vapor flows to such a portion of the container at the side of the fins 9 as has a lower temperature. The vapor of the working fluid is condensed because its heat is taken by the atmosphere. Specifically, the heat of the CPU 7 is delivered by the working fluid of the heat pipe 6 until it is radiated from the fins 9. As a result, the temperature of the CPU 7 is suppressed within an allowable range. Incidentally, the working fluid thus condensed into liquid phase is sucked by the capillary pressure of the wick into the container inner wall at the evaporation side, where it is evaporated again.
Since the space in the personal computer provided for the heat pipe is seriously restricted, as described above, the heat pipe to be used has to be small in section. On the other hand, the heat radiating portion and the heat radiating portion are spaced at a distance so that the heat pipe has a considerable length, as compared with its sectional area (i.e., its effective area for the passage).
In view of this, according to the prior art, groove wicks are formed to establish a desired capillary pressure (or pumping action) while retaining the vapor passage. However, the capillary pressure to be established by the groove wicks is not high, but the reflux distance of the working fluid used in the personal computer cooling heat pipe is relatively long. Thus, the heat pipe 6 of the prior art may fail to achieve a necessary and sufficient cooling capacity. In case, more specifically, the heat flux is increased with the high power of the CPU 7, the pumping action for the working fluid in liquid phase may become insufficient to dry out and make the evaporation portion short of the working fluid.
Because of a small sectional area, as described above, the working liquid being returned is splashed out as the flow rate of the working fluid vapor rises. This splash may also make the evaporation portion short of the reflux of the working liquid. After all, the heat transfer characteristics may become too low to cool the CPU 7 sufficiently.
Moreover, the cooling capacity of the CPU 7 through the heat pipe 6 is restricted by the substantial area of heat radiation of the heat pipe 6. Since the cooling device of the prior art is constructed to retain the area of the heat radiating portion of the heat pipe 6 by the fins 9, the heat radiation area required of the heat pipe 6 increases with the rise of the output of the CPU 7 so that the size of the fins 9 has to be enlarged. Since, moreover, these fins 9 are disposed in the personal computer body 1, the space for the cooling device to occupy in the inside space of the personal computer body 1 is necessarily enlarged. This invites a disadvantage that the size of the personal computer body 1 is accordingly enlarged.
For manufacturing the aforementioned flattened heat pipe 6, on the other hand, not only a mass production is desired at a reasonable cost and at a high rate, but also a predetermined sectional shape (for the vapor passage) has to be retained. These requirements have not be satisfied by the process of the prior art.
Incidentally, the means known per se for grading up the functions of the personal computer is exemplified by replacing the display section 3. At this time, the display section 3 and the personal computer body 1 are naturally separated from each other. In the case of the aforementioned cooling device, the display section 3 is detached from the personal computer body 1 by disassembling the hinge 3a by means of a suitable tool. Thus, in the cooling device thus far described, it is not easy to remove the display section from the presomal computer body 1 and it has low detachability.